It has been found that the performance of the pervaporative separation of hydrocarbon feeds containing mixtures of aromatics and non-aromatics is highly dependent on the oxygen content of the hydrocarbon feed.
U.S. Pat. No. 5,095,171 teaches that the separation of aromatic hydrocarbons from mixtures of aromatic and non-aromatic hydrocarbon feeds under pervaporation conditions is improved by the control of the amount of oxygen present in the feed. The amount of oxygen in the feed, such as heavy cat naphtha or other cracked feed, should be less than 50 wppm, preferably less than 10 wppm. The oxygen level in the feed is controlled by preventing exposure of the feed to air or oxygen, or, in the case of a feed which is already contaminated with oxygen, by addition to the feed of an oxygen scavenger or inhibitor. Oxygen scavengers or inhibitors are selected from the group consisting of hindered phenols, hindered amines and mixtures thereof.
The procedure of U.S. Pat. No. 5,095,171 while useful is hindered by the disadvantage of the need for segregated, oxygen free tankage and piping, which is expensive and may not always be available. Further, maintaining a continuous oxygen free environment over the feed may not be possible. Minor air leakages can create significant process problems during subsequent pervaporation. In such instances the oxygen scavenger or inhibitor can be used but their use should be kept to a minimum as their long term effects on the membranes used in the pervaporation process has not been established.
It is desirable therefore to identify alternate ways for reducing the oxygen content of hydrocarbon feeds containing mixtures of aromatic and non-aromatic components which are subjected to the pervaporative separation of the components present in the feed.